In recent years, many countries of the world have devoted great energies to research and develop clean alternative energy and techniques for storage of energy, in order to solve problems in relation to air pollution and/or global warming. In particular, electric energy storage technologies including, for example, a high-capacity power storage system for storing electric energy generated by a variety of alternative energies, different kinds of mobile devices, a small size but high-energy power storage system required for future electric vehicles for reducing atmospheric pollution, or the like, were being raised as a key point of the foundation of the future green industry. Most of such future technologies for power storage are based on the use of principles of ion absorption (charge) and desorption (discharge) such as a Li ion battery or super capacitor, therefore, all countries of the world are proceeding with significant research and development efforts to accomplish high-efficiency densification and extension of capacity by improving charge-discharge characteristics of materials and parts.
Meanwhile, the same principles as described above have also been recently employed in water treatment applications including treatment of purified water or waste water, sea water desalination, etc., whereby a method of treating water with a very decreased energy cost, compared to existing evaporation or reverse-osmosis (RO), that is, a capacitive deionization (CDI) process is now under development.
For a power storage and water treatment system using the same principles as described above, the most significant problem is high equipment costs as well as reduction of efficiency in the extension of capacity. In other words, due to an increase in an area of an electrode for scaling-up, an irregularity of an electrical field distribution in the electrode caused thereby, a limited amount of an active material in a thin film electrode coated on a collector, a decrease in a contact area between the active material and an electrolyte by a binder during coating, and a deterioration of charge-discharge efficiency, so forth, a number of unit cells must be stacked to hence cause high equipment costs and, specifically, a capacitive deionization (CDI) process encounters a problem of increasing operation costs due to pressure loss of water (electrolyte) in the stack flow.